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I have recently purchased an 1890 2200 sq ft farm house with approx 1200' on 1st fl and 1000' on 2nd fl. Half of the basement is a full but unfinished basement and half is crawl space and the attic is fairly empty and unfinished except it has pine floor boards and has a steep pitch from the middle towards each of the 4 corners.

The heat is a closed water system w/ exposed radiators in the extension areas (prob built 50+ yrs ago) and the main part of the house has built in radiators. I'm told to keep this radiator system as it gives off comfortable heat vs forced air systems.

The question I have is whether high velocity a/c systems make sense or should I do a ductless system. My main concerns are taking up too much space in the attic w/ ductwork and air handlers, cost of system, ability to cool the house, and noise of system.

By ductless, you mean using mini-splits? Problem here is it gets expensive if you need to install several of them to do all of the house. Do you want 4 or 5 condenser units outside the home? They're better suited for cooling a specific room.

The HV AC systems are pricey and usually used in re-habs when yoo want to use up little closet space getting ducts down from the attic or up from the basement to the 2nd floor.

It might price out easier to just get 2 small split AC systems: one in the attic for the 2nd fl and 1 in the basement for the 1st (and basement when finished?) This is the best zoning option.

Any thoughts on the high velocity mini duct systems such as Unico or Spacepak. I thought maybe I could put 1 air handler in the basement and run 1st and 2nd floor system from there vs 2 split systems. Any benefits/negatives with this solution?

AC works better from the attic. Cold air wants to fall not rise and your 2nd floor probably has the larger cooling load. Spacepak and Unico are great systems if you find a contrator that knows these systems well. Remember you loose SEER rating with a HV system. Just price it out both ways. HV is last resort system when a regular duct system can't be done, IMO.

unico systems

I've designed and helped install unico systems for the last 15 years and find it to be IMO the best a/c system out there. Because of the HV system delivers air by aspiration not diffusion it makes no difference whether the system is in the attic or basement. The system is very quiet also when you put in an average of 7 outlets per ton.

Insulate under the floor, typically the best way to do it in the older homes unless there is a clear path to block off all the air that will get under the attic floor. Have the duct system in the conditioned space is best and there is no reason not to put the HV system in the basement unless head space is an issue.